prevent executor self-links in JIT cold exits

Author: cocolato

Include/internal/pycore_uop_metadata.h

@@ -12,7 +12,7 @@
 
 from test.support import (script_helper, requires_specialization,
                           import_helper, Py_GIL_DISABLED, requires_jit_enabled,
-                          reset_code)
+                          reset_code, SHORT_TIMEOUT, isolation)
 
 _testinternalcapi = import_helper.import_module("_testinternalcapi")
 
@@ -6225,6 +6225,28 @@ def __exit__(self, e, v, t): ...
                 f1()
         """), PYTHON_JIT="1")
 
+    @isolation.runInSubprocess(timeout=SHORT_TIMEOUT)
+    def test_for_iter_side_exit_does_not_self_link(self):
+        def exhaust(iterator):
+            for _ in iterator:
+                pass
+
+        values = range(TIER2_THRESHOLD)
+        # After the initial trace, MAX_CHAIN_DEPTH side exits cause the final
+        # executor to be installed at FOR_ITER.
+        warmup_iterators = (
+            iter(set(values)),
+            iter(dict.fromkeys(values)),
+            iter(values),
+            enumerate(values),
+            zip(values, values),
+        )
+        for iterator in warmup_iterators:
+            exhaust(iterator)
+
+        # A different iterator type must not link that executor to itself.
+        exhaust(map(bool, values))
+
 def global_identity(x):
     return x
 

Lib/test/test_capi/test_opt.py

@@ -6262,6 +6262,10 @@ dummy_func(
             if (target->op.code == ENTER_EXECUTOR) {
                 PyCodeObject *code = _PyFrame_GetCode(frame);
                 executor = code->co_executors->executors[target->op.arg];
+                if (executor == _PyExecutor_FromExit(exit)) {
+                    _Py_ExecutorDetach(executor);
+                    GOTO_TIER_ONE(target);
+                }
                 Py_INCREF(executor);
                 assert(tstate->jit_exit == exit);
                 exit->executor = executor;